Absolutely Christmas! Nearly all my favorite memories of annual tradition are tied to it. Plus everyone has some kind of minty chocolate shake or pumpkin flavored something. That's right! I'm one of those guys! Bring on the pumpkin spice!! Did I mention I love eggnog? Of all the conspiracies to exist, why does one of them have to keep eggnog from us except near Christmas time?
But on a more serious note, I love that while I'm celebrating Christmas with my family here in the U.S. someone else in some other part world is celebrating something. I love that nearly everywhere in the world you can find people celebrating at that time of year. I don't care what they call it. It's the time of year where everyone takes a moment to spend time with family to give to each other to forget about work, politics, and their diets.
The world isn't perfect. None of us will ever have a perfect life, But there are moments like when you achieve a lifelong goal or you become a parent for the first time when everything just seems right. Life may not be perfect, but I think we can find moments that are. And at Christmas or quanza, or whatever you celebrate it's almost like for a moment the whole of humanity takes one big collective breath and finds that perfect moment together.
No matter what you believe, I feel like that alone is something we can take with us throughout the year and make the world a better place.

Christmas, as well; it is, as Robert said, a time when there's almost a universal sense of celebration in nearly every culture, and in nearly every place in the world.

The way our family celebrates Christmas, we try to keep that celebration going as long as possible. This begins on the 24th; Christmas Eve dinner with my wife's family tends to follow Slavic tradition (e.g. meatless, except for seafood; twelve dishes to represent the Twelve Apostles). Then there'll be another big dinner on the 25th, and my family will typically throw down yet another big feast on Boxing Day. There'll be something around New Year's as well, and then my wife and I will typically host our friends and neighbours at our place early in January for "Ukrainian Christmas" (which is actually when Christmas is observed in all the Eastern churches, not just in the Ukraine).

Technically, the Christmas season - if you go by church calendars - lasts until February 2nd (which used to be called Candlemas). And we'll tend to keep the decorations up until then, and find as many opportunities as we can over the month of January to meet up with friends and family for big dinners and other celebrations.